1. Field of the Invention:
This invention relates generally to presses for metal working, and more particularly to lower die holders for press brakes or the like.
2. Description of the Prior Art: In the typical press brake of the mechanical type (i.e. crankshaft and connecting rod drive of ram, as distinguished from hydraulic drive of ram) the height of the lower die, or the height of the upper die (punch) in the ram, is adjusted by trial-and-error, depending upon the thickness of the stock to be bent, the shape of the die, and the tonnage limitations of the machine, for example. Where a series of bends is to be performed on a single workpiece, inconvenience is encountered when different bends to be made are of different lengths. Therefore, the die adjustment must be made to accommodate the longest bend without excessive tonnage, with typical result often being that the shortest bend is not of the desired shape or consistency from one workpiece to the next. Also, it is sometimes desirable to make a bend to an angle considerably greater than the included angle of die, but there is no provision for facilitating the inclusion of this type of bend (sometimes referred to as an "air" bend) along with a series of full depth bends in a sequence of bends in a workpiece. Therefore, mechanical press brakes do not have the versatility conferred to hydraulic press brakes by the gauging system disclosed in my U.S. Pat. No. 3,618,349, issued Nov. 9, 1971.
A further problem sometimes encountered with mechanical press brakes is the tendency of the central portion of the die or bed to deflect more than the edge portions. Efforts to solve this problem are exemplified in U.S. Pat. No. 2,199,864 to Wehr, that discloses an adjustable bolster block to compensate for deflection in the bed and/or ram of the press so that articles bent thereon will be of uniform angle from end to end, and an adjustable bolster block disclosed in U.S. Pat. No. 2,456,856 to Bath. Otherwise, the conventional practice is to insert shims where needed between the lower die and die holder to provide the needed support to offset the deflection. A recently issued patent providing means for adjusting a stop bar in the bottom of the die, but not the whole die itself, is U.S. Pat. No. 3,844,156 to Hanni and Gygli.
Accordingly, there remains the need for a solution of one or more of the aforementioned problems of mechanical press brakes and, in addition, it would be quite helpful to provide some means facilitating release of a mechanical press brake which has been overloaded during the descent of the ram, and thereupon becomes stuck.